Arteries have the function of carrying oxygenated blood away from the heart to the entire body through the main artery, aorta. Aorta further leads to smaller arteries called arterioles that diverge into capillary beds. These smaller capillaries branch among the cells and tissues of the body.

The arterial system of human body branches out from one main artery called as the dorsal aorta. Similar to veins, arteries also have three layers of tissue, an outer layer made up of tissues, inner layer comprising of epithelial cells and in between lies a layer of muscles.

Capillaries' function is to carry blood away from the body and at cellular level, it exchanges nutrients, waste, and oxygen with tissues. Capillaries contain one layer of cells called the endothelial tunic where diffusion and exchange of materials takes place.

Arteries supply pure oxygenated blood to the capillaries which reaches to various tissues and cells of the body where exchange of oxygen and carbon dioxide takes place. Capillaries are connected to both veins and arteries thus playing the dual role in exchange oxygen as well as carbon dioxide. Capillaries are very delicate, sometimes as thin as one epithelial cell so that blood can easily pass through them. The oxygen released from these blood cells pass through the capillary walls into neighboring tissues. The carbon dioxide released from the tissues enters the capillary walls in the red blood cells and from there reaches to veins. These veins then transport deoxygenated blood to the heart and lungs after receiving it from the capillaries.

Veins are blood vessels that bring deoxygenated blood back to the heart and drain out impure blood from organs and limbs. Both veins and arteries have two more tunics surrounding the endothelium. The middle tunica layer is made up of smooth muscle regulating blood flow whereas the outer tunica externa is composed of connective tissue that supports blood vessels. Valves are present inside the veins which helps blood move in one direction.